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	<PARAM NAME="Keyword" VALUE="Tram services">
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<P><B><A NAME="5.3"></A>5.3  Headcodes</B></P>

<P>Headcodes (i.e. the last four characters in a service reference) must consist of four consecutive alphanumeric characters, i.e. capital or small letters, or digits.  The only restriction is that repeating services with increasing digits between repeats (<A HREF="5.74ptj.htm">see section 5.7</A>) must contain digits as the last two characters.  The standard British headcode consists of 'digit letter digit digit', but other systems use different formats.</P>

<P>See <A HREF="5.111w8h.htm">section 5.11</A> for some important aspects that will help to avoid errors. </P>

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